Many gelled cosmetic emulsions rely on gellants, waxes, fillers, heavy oils, and plasticizers for developing the structure to make a gel or stick composition. The structure built by these agents and materials give the product a balance of rigidity and firmness depending on the desired product. For example, the structure of lipstick is traditionally formed by a blend of wax and oil. However, these adjuvants, particularly waxes, have a disadvantage in that they contribute to opacity which diminishes the color of the pigment. The product therefore, has a dull, lackluster and pale appearance. To overcome this problem, enhanced amounts of pigment are added to the composition. Another drawback to the addition of wax is that it adheres poorly to the skin and compromises the longevity of wear of the product. For example, many commonly used cosmetic products, such as foundation, concealer, eyeliner, and lipstick, which contain these materials, are subject to fading, smudging, and flaking. Such products also have a matte appearance that is not always desirable. In addition, other adjuvants such as heavy oils can feel uncomfortable on the skin and have a distinct oily feel that may also be unpleasant. Therefore, to address these issues, alternative gelling agents have been sought and specific polyamides have been used to gel cosmetic products.
The use of polyamides in cosmetic products has been known. For example, polyamide resins have been used in an anhydrous lipstick as disclosed in U.S. Pat. No. 3,148,125. The method of making polyamides is disclosed in, for example, U.S. Pat. No. 2,450,940. The polyamide resin has also been used in a deodorant or antiperspirant gel or stick as disclosed in U.S. Pat. Nos. 4,275,054 and 5,500,209 because of its odor absorbing properties. None of these references, however, discloses a stable emulsion gelled with a stable polyamide. The stick, soft gel, or clear gel compositions disclosed in, for example, U.S. Pat. Nos. 6,051,216, 5,603,925, and 5,998,570 and European Patent Application Nos. EP 1 068 855 and EP 1 068 856 are unstable emulsions, single phase compositions, or use a siloxane based polyamide. The siloxane polyamides have been developed because of their alleged ability to, in addition to gel the composition, provide a less tacky composition. However, the siloxane based polyamides are not compatible with a wide variety of oils, for example, hydrocarbon oils (except low molecular weight), and because they are less tacky, their adhesion properties are significantly impaired, making them less desirable in products that require minimally an initial phase of adhesion during the application of the product to the skin or hair. Therefore, it is desirable to use other polyamides in cosmetic emulsion systems because products such as mascara, for example, need a certain degree of tackiness when being applied but afterwards, upon drying the tackiness of the mascara needs to transition to a comfortable feel on the lashes. Until now, it has not been known to fine-tune the tacky nature of a cosmetic dual phase product containing the polyamide resin as a gelling agent. The compositions heretofore have either been too tacky or not tacky enough for products that need to exhibit varying degrees of tackiness over time and during their use. Thus, the emulsions of the present invention gelled with a polyamide based gelling system have heretofore not been known. A need for a stable cosmetic emulsion gelled by a stable polyamide resin system that adheres to the skin and functions in a variety of cosmetic emulsion systems still remains. The emulsion system of the present invention is also desirable because it allows water-soluble ingredients to be incorporated into the product containing the emulsion.
An ester terminated polyamide (ETPA) of U.S. Pat. No. 6,111,055 comprises molecules of the formula (I),
wherein n designates a number of repeating units such that ester groups constitute from 10% to 50% of the total of the ester and amide groups; R1 at each occurrence is independently selected from an alkyl or alkenyl group containing at least 1 carbon atom, preferably at least 4 carbon atoms; R2 at each occurrence is independently selected from a C4-42 hydrocarbon group with the proviso that at least 50% of the R2 groups have 30-42 carbon atoms; R3 at each occurrence is independently selected from an organic group containing at least two carbon atoms in addition to hydrogen atoms, and optionally containing one or more oxygen and nitrogen atoms; and R3a at each occurrence is independently selected from hydrogen, C1-10 alkyl and a direct bond to R3 or another R1a such that the N atom to which R3 and R3a are both bonded is part of a heterocyclic structure defined in part by R3a—N—R3, such that at least 50% of the R3a groups are hydrogen.
However, it has been surprisingly found that when the number of carbon atoms in the R1 group is increased above 4, and preferably has at least about 10 carbon atoms, more preferably at least about 12 carbon atoms, then ETPA is an excellent gellant for aliphatic hydrocarbon. The upper range for the number of carbon atoms in the R1 group is not particularly critical, however preferably the R′ group has less than or equal to about 24 carbon atoms, and more preferably has less than or equal to 22 carbon atoms. R1 groups having about 16-22 carbon atoms are highly preferred. The identity of R1 at any occurrence is independent of the identity of R1 at any other occurrence.
The R2 group in formula (I) is suitably a hydrocarbon containing 4 to 42 carbon atoms. A preferred R2 group contains 30-42 carbon atoms (i.e., is a C30-42 group), and at least 50% of the R2 groups in an ETPA gellant preferably have 30-42 carbon atoms. Such R2 groups are readily introduced into an ETPA when the gellant is prepared from polymerized fatty acid, also known as dimer acid. Typical unsaturated fatty acids used to form polymerized fatty acid include oleic acid, linoleic acid, linolenic acid, etc. Tall oil fatty acid, which is a mixture containing long-chain unsaturated fatty acids obtained as a byproduct of the wood pulping process, is preferred for preparing polymerized fatty acid useful in ETPA formation.
In one embodiment, all of the R3a groups in an ETPA gellant are hydrogen, so that R3 alone joins the two nitrogen atoms shown in the formula —N(R3a)—R3N(R3a)—. In this case, the R3 group contains at least two carbon atoms, and optionally oxygen and/or nitrogen atoms, in addition to any hydrogen atoms that are necessary to complete otherwise unfilled valencies of the carbon, oxygen and nitrogen atoms. In a preferred embodiment, R3 is a hydrocarbon group, having 2 to about 36 carbon atoms, preferably having 2 to about 12 carbon atoms, and more preferably having 2 to about 8 carbon atoms.